For a ladle for steel making, refractory bricks or castable materials which are a monolithic refractory have hitherto been used as a lining refractory. Under those backgrounds, in integrated iron mills in Japan, a method for forming a lining by casting a castable material on the spot of use is the main current.
As to the quality of castable materials, in recent years, alumina-magnesia materials composed mainly of alumina and magnesia are widely used. Alumina and magnesia are composed of a corundum crystal and a periclase crystal, respectively, and these react with each other at a high temperature during the use of a kiln such as ladles, thereby forming a spinel crystal while being accompanied with volume expansion. Following this change of crystal, a minute spinel-containing layer is formed in the vicinity of the working surface of a high temperature, and therefore, such an alumina-magnesia material has characteristic features that it is very small in infiltration of slag and excellent in resistance against slag corrosion. Moreover, such an alumina-magnesia material does not contain carbon, and therefore, especially in case of receiving or refining a low-carbon molten steel, it also has a characteristic feature that staining of the steel to be caused due to lining refractories can be eliminated.
However, in order to form a ladle lining refractory by casting, a number of machine equipment inclusive of a mixer for kneading a castable material with water on the spot of construction, a metallic frame for constructing a kneaded material in a prescribed thickness, a distributor for uniformly inputting a kneaded material in a frame and a vibrator for obtaining a constructed body having sufficiently uniform quality and high degree of packing should be prepared.
Furthermore, since the castable material after the construction contains water, drying equipment for heating and drying step-by-step is necessary. In the case where the rate of drying is too fast, since water vapor explosion is often generated by water in the constructed body, this drying equipment should have specifications such that the temperature can be satisfactorily controlled. The performance of the castable material as a refractory is ultimately determined by whether the construction on the spot and the drying state are good or bad.
On the other hand, in many electric furnace iron mills in Japan and almost all of iron mills in Europe and North America, bricks are used for a ladle lining material.
The reasons why the brick construction is performed instead of casting reside in the matter that special equipment or apparatus should be set up for the foregoing construction or drying; the matter that the construction on the spot which affects the performance of the lining material is uneasy; and the like.
As to the quality of bricks which are used for ladles, high-alumina or carbon-containing bricks are the main current, and alumina-spinel materials are used in part of iron mills.
Also, in Patent Document 1, unburned alumina-magnesia bricks using a resin as a binder for alumina and magnesia are proposed.
Furthermore, in Patent Document 2, unburned alumina-magnesia based bricks using a coarse magnesia raw material and a spinel raw material of not more than 1 mm are disclosed.
Patent Document 1: JP-A-63-151661
Patent Document 2: JP-A-2000-272956